We analyze recent torque measurements of the magnetization Md vs magnetic field H in optimally doped YBa2Cu3O 7-y (OPT YBCO) to argue against a recent proposal by R. I. Rey that the magnetization results above Tc are consistent with Gaussian fluctuations. We find that despite its strong interlayer coupling, OPT YBCO displays an anomalous nonmonotonic dependence of Md on H which represents direct evidence for the locking of the pair wave function phase θn at Tc and the subsequent unlocking by a relatively weak H. These unusual features characterize the unusual nature of the transition to the Meissner state in cuprate superconductors. They are absent in low-Tc superconductors to our knowledge. We also stress the importance of the vortex liquid state, as well as the profiles of the melting field Hm(T) and the upper critical field curve Hc2(T) in the T-H plane. Contrary to the claims of Rey, we show that the curves of the magnetization and the Nernst signal illustrate the inaccessibility of the H c2 line near Tc. The prediction of the Hc2 line by Rey is shown to be invalid in OPT YBCO.
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Feb 19 2013|
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics